Grating and clean room system comprising the same

ABSTRACT

Grating forming the floor of a clean room minimizes turbulence and enhances the rate at which air is discharged therethrough. The grate includes a base plate having a plurality of through-holes. Each of the through-holes includes a receiving portion through which the air is received and an exhausting portion through which the air is exhausted. The cross-sectional area of the receiving decreases toward the exhausting portion, and the cross-sectional area of the exhausting portion decreases toward the receiving portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a clean room such as that in whichsemiconductor devices and liquid crystal displays (LCD) aremanufactured. More particularly, the present invention relates to thegrating that forms a floor of a clean room system.

2. Description of the Related Art

Semiconductor devices and liquid crystal displays (LCD) must bemanufactured under very precise processing conditions. Therefore, theyare fabricated in extremely clean environments unlike many commonproducts of manufacture. In this respect, several semiconductorprocessing apparatuses are typically provided in separate clean rooms inwhich the environments are maintained so as to be extremely clean.

In a clean room, technicians work in special dustproof clothes in orderto minimize the production of foreign substances such as dust. Also, theupper portion of the clean room is maintained at a pressure slightlyhigher than the pressure prevailing at the bottom of the clean room suchthat air (clean air) flows downwardly in the clean room. Grates (panelshaving holes) provide the floor of the clean room such that the air isdischarged through the floor. Therefore, contaminants entrained by theair in the clean room are directed toward the floor of the clean roomand are discharged to the outside through the holes of the grating.

However, unlike micro-particles, molecular contaminants in the air ofthe clean room, referred to as nanoparticles, and airborne molecularcontamination (AMC) are not easily removed. In fact, the differentialpressure and velocity of the airflow required in the clean room for thenanoparticles and the AMC to be removed must be at least 18% higher thanthat under which micro-particles are removed. Needless to say, theoperating costs of running the air conditioning system of the clean roomsystem to provide such a high differential pressure and airflow velocityare very high. Also, a conventional clean room system that is capable ofproducing the differential pressure and airflow velocity required forthe removal nanoparticles and AMC is very expensive to manufacture.

Also, as illustrated in FIG. 1, eddies are generated when the air passesvertically through the holes in the grating. The eddies are mainlygenerated at edges of the grates that define the entrances and exits ofthe holes, as shown with dotted lines.

To conform the effects of these eddies, particles (30,000 to 35,000counter/cf) were produced at a height of 0.2 m above the conventionalgrating in a clean room. FIG. 2 illustrates the results of counting thenumbers of the particles (30,000 to 35,000 counter/cf) at respectiveheights in the clean room. As is clear from the results shown in FIG. 2,the particles were distributed to a height of 70 cm due to the eddies.

That is, the eddies generated around the holes of the grating preventthe air from being rapidly exhausted and cause contaminants (inparticular, the nanoparticles and the AMC) to reach a height of up to 70cm from the grating (the floor). As a result, the air is contaminated atthe level at which the processes in the clean room are carried out.

SUMMARY OF THE INVENTION

An object of the present invention to provide a grate that facilitates asmooth and/or rapid discharging of air from a clean room.

Likewise, another object of the present invention is to provide a cleanroom system in which air can be discharged smoothly and/or rapidly fromthe clean room thereof, and which system does not require an expensiveair conditioning system.

It is another object of the present invention to provide a grate capableof minimizing eddies in air traveling therethrough to preventcontaminants from being blown upwardly.

According to one aspect of the present invention, a grate used flooringin a clean room comprises a base plate having a plurality of holes thatact as nozzles through which the air in the clean room is discharged.

According to another aspect of the present invention, a clean roomsystem comprises a clean room, an air supplying portion including a fanand/or a filter in the ceiling of the clean room to supply clean airinto the clean room, and an exhausting portion including gratingdisposed in the floor of the clean room, the grating defining aplurality of holes through which the air inside the clean room isdischarged, and the cross-sectional area of each hole first decreasingand then increasing in a direction from the top (one side) to the bottom(other side) of the grating.

Each of the holes has a receiving portion through which the air isreceived and an exhausting portion through which the air is exhausted.The cross-sectional area of the receiving portion decreases in adirection toward the exhausting portion. The cross-sectional area of theexhausting portion decreases in a direction toward the receivingportion.

The surfaces that define the receiving portion and the exhaustingportion of each hole are frusto-conical or curved. Also, thecross-sectional shape of the holes may be circular or elongate. Stillfurther, each hole may also have a middle portion extending a finitedistance between the receiving portion and the exhausting portion. Themiddle portion has a uniform cross-sectional area.

The grate or grating may also comprise a tile of polyvinyl chloride atthe top thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in further detail withreference to the accompanying drawings. In the drawings:

FIG. 1 is a sectional view of a conventional grate forming the floor ofa clean room;

FIG. 2 is a graph illustrating the distribution of certain particlesthroughout the height of a clean room whose floor is formed byconventional grating;

FIG. 3 schematic diagram of a clean room system according to the presentinvention;

FIG. 4 is a perspective view of an embodiment of a grate (panel) for usein the floor of a clean room according to the present invention;

FIG. 5A is a plan view of a portion of the grate according to thepresent invention;

FIG. 5B is a sectional view of the grate taken along line B-B′ in FIG.5A;

FIG. 6 is a graph of the differential pressure in a clean room having afloor formed by the conventional grating and the differential pressurein a clean room having a floor formed by grating according to thepresent invention;

FIG. 7 is a perspective view of another embodiment of a grate (panel)according to the present invention;

FIG. 8 is a graph illustrating the turbulent kinetic energy K1 of airpassing through the conventional grating panel and the turbulent kineticenergy K2 of air passing through the grating according to the presentinvention;

FIG. 9 is a graph illustrating the distribution of certain particlesthroughout the height of a clean room whose floor is formed by gratingaccording to the present invention as compared with the distributionshown in FIG. 3;

FIG. 10 is a partial sectional view of another embodiment of a grateaccording to the present invention; and

FIG. 11 is a sectional view of still another embodiment of a grateaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in more detail withreference to FIGS. 3 to 11. Like reference numerals are used todesignate like elements throughout the drawings.

Referring first to FIG. 3, a clean room system 100 includes a cleanroom, an air supplying portion and an air exhausting portion. The airsupplying portion includes a fan filter unit 120 provided in the ceilingof the clean room 110. The fan filter unit 120 includes a filter and afan integrated as a unit so as to supply filtered air into the cleanroom. Although not shown, a ceiling filter, such as a high efficiencyparticulate air (HEPA) filter or an ultra low penetration air (ULPA)filter, may be provided in the ceiling of the clean room for removingfrom the air foreign particles, such as dust, whose average diameter ison the order of several microns.

The air passes through the fan filter unit 120 and into the clean room110 where the air forms a vertical current. Such a vertical currentforces the contaminants generated in the clean room 110 to the floor toprevent the contaminants from remaining at the level at which themanufacturing processes are performed. In particular, such contaminantsare discharged together with the air through a grate 130 of the airexhausting portion. The grate 130 is supported by a supporting structure114 above a sub-floor 112 of the air exhausting portion. Also, the grate130 has holes therethrough so that the air can be discharged from theclean room into a region between the grate 130 and the sub-floor 112.The air discharged through the grate 130 is drawn to the ceiling by thefan filter unit 120 and is re-circulated through the clean room by thefan filter unit 120. Accordingly, the environment within the clean roomis maintained extremely clean.

The grate 130 will now be described in more detail referring to FIGS. 3and 4.

The grate 130 includes a base plate 132 made of steel, stainless steel,or aluminum. Other materials such as a composite material may be used.The grate 130 may be attached to the supporting structure 114 or mayrest freely on the supporting structure 114. In any case, the grate 130may be easily removed from the supporting structure to allow access towiring, ductwork, or other infrastructure 116 in the region between thegrate 130 and the sub-floor 112.

The grate 130 also includes a tile 133 made of polyvinyl chlorideattached to the top surface of the base plate 132 so as to provide aprotective surface. Also, the grate 130 may be processed so as toprovide any number of desired surface characteristics. For example, thebase plate 132 may covered with carpet or other flooring material fordecorative and functional reasons such as to provide sound attenuationand conductivity control. Also, the base plate 132 may be coated withepoxy or may be gold-plated to provide desired characteristics such asstatic control, abrasion resistance, and protection against chemicals.

Referring to FIG. 4, the size of the grate 130 is typically 600 mm×600mm. However, the grates may have other sizes such as 750 mm×750 mm or500 mm×500 mm because the base plates, at least, can be easily formed bya molding process. In any case, the grate 130 may be sized according tothe supporting structure 114 of the clean room system.

The grate 130 also has a plurality of holes 134 that extendtherethrough. The holes 134 constitute channels through which the airinside the clean room is discharged to the outside (the region justabove the sub-floor). The holes 134 are arranged in a pattern that isboth attractive and facilitates the flow of the air through the grate.According to an embodiment of the present invention, the total area ofthe openings of the holes 134 at the top of the grate accounts for about18% of the total area of the top.

Referring now to FIGS. 5A and 5B, each of the holes 134 includes areceiving portion 136 open at one side of the grate and through whichthe air is received, and an exhausting portion 138 open at the otherside of the grate and through which the air is exhausted. The receivingportion 136 is tapered such that the cross-sectional area thereofbecomes smaller in a direction toward the exhausting portion 138.Similarly, the exhausting portion 138 is tapered such that thecross-sectional area thereof becomes smaller in a direction toward thereceiving portion 136. The diameter of the narrowest portion L2 of thehole 134 is about 8.5 mm (equal to the diameter of the holes of theconventional grate). The diameter of the widest portion L1 of the holeis about 10 mm. Although the holes 134 are shown as being round in FIG.5A, the holes 134 may be elongate (in the form of slots) as illustratedin FIG. 7.

The flow of the air that passes through the holes 134 is illustratedwith dotted lines in FIG. 5. As can be seen from FIG. 5, the hole 134 isformed such that a frusto-conical surface 136 a defines the receivingportion 136 such that the surface 136 a is inclined relative to thedirection of flow of the air through the clean room. Accordingly, theair that collides with inclined surface 136 a is introduced toward theexhausting portion 138 along the surface 136 a such that the air flowssmoothly in the receiving portion 136 of the hole. Similarly, afrusto-conical surface 138 a defines the exhausting portion 138 suchthat the width of the exhausting portion 138 a increases in thedirection of the air flow. Accordingly, the air that flows from thereceiving portion 136 to the exhausting portion 138 is rapidlyexhausted.

FIG. 6 shows a comparison of the differential pressure in a clean roomQ1 whose floor is formed by the conventional grating and thedifferential pressure of a similar clean room Q2 whose floor is formedby grating according to the present invention. As can be seen from FIG.6, the pressure drop inside the clean room Q2 is 2.379 Pa greater thanthe pressure drop inside the clean room Q1 (an improvement of 42%). Suchan improvement offered by the present invention is due to a nozzle(venture) effect provided by the holes 134, wherein turbulence andpressure increases are minimized. In particular, eddies are hardlygenerated at the edges of the grate that define the entrances and exitsof the holes 134. Therefore, contaminants (in particular, nanoparticlesand AMC) can be rapidly removed from the clean room through the grate130.

Also, the lack of turbulence prevents the contaminants from being blownup to a critical height in the clean room. In this respect, FIG. 8 showsa comparison between the turbulent kinetic energy K1 of air passingthrough the conventional grating and the turbulent kinetic energy K2 ofair passing through grating according to the present invention. As canbe seen from FIG. 8, the turbulent kinetic energy K2 is 37% less thanthe turbulent kinetic energy K1. Thus, the differential pressure in aclean room whose floor is formed by the grating according to the presentinvention is greater than that in a comparable clean room whose floor isformed by the conventional grating. Likewise, the mass flow of air in aclean room whose floor is formed by the grating according to the presentinvention is greater than that in a comparable clean room whose floor isformed by the conventional grating.

FIG. 9 illustrates a comparison of the numbers of particles at therespective heights in a clean room whose floor is formed by the gratingaccording to the present invention and in a comparable clean room whosefloor is formed by the conventional grating. For the purposes ofproviding this comparison, particles of 30,000 to 35,000 counter/cf wereproduced at a height of 0.2 m above the grating. Also, the air velocityin the fan filter unit 120 was 0.4 m/s. As can be seen from FIG. 9, thecritical height when the grating according to the present invention wasused was 40 cm less than the critical height when the conventionalgrating was used.

FIG. 10 illustrates a grate 130 a similar to that of the above-describedgrate 130 with the exception of the shape of the holes 134. The holes134 a of the grate 130 a each have a receiving portion 136, anexhausting portion 138, and a middle portion 140 interposed between thereceiving portion 136 and the exhausting portion 138. The cross sectionof the middle portion 140 extends straight (parallel to the direction ofair flow in the clean room) and is uniform between the receiving portion136 and the exhausting portion 138. The flow of the air in the hole 134a is similar to the flow of the air in the hole 134 described above inconnection with FIGS. 5A and 5B.

FIG. 11 also illustrates a grating panel 130 b similar to that of theabove-described grate 130 with the exception of the shape of the holes134. In this case, the holes 134 b of the grate 130 b are curved. Morespecifically, each hole 134 b includes a receiving portion 136 b throughwhich the air is received and an exhausting portion 138 b through whichthe air is exhausted. The surface of the base plate defining thereceiving portion 136 b is curved such that the cross-sectional area ofthe receiving portion 136 b decreases in a direction toward theexhausting portion 138 b. Likewise, the surface of the base platedefining the exhausting portion 138 b is curved such that thecross-sectional area of the exhausting portion 138 b decreases in adirection toward the receiving portion 136 b. Such curved holesfacilitate a smooth flow of the air (illustrated with dotted lines) likethe holes 134.

As described above, the turbulent kinetic energy of air flowing throughthe grate according to the present invention is minimized and hence, theair flow rate is maximized and the pressure drop loss is minimized.Therefore, the critical height of the particles above the grate isrelatively low, e.g., lower by about 40 cm when compared to the priorart. Thus, the present invention is effective in controlling thenanoparticles and AMC in a clean room.

Finally, although the structure and function of the grating clean roomsystem using the grating according to the present invention have beendescribed above with reference to the preferred embodiments thereof,various changes in form and details thereto will be apparent to those ofordinary skill in the art. Accordingly, various changes can be made tothe preferred embodiments without departing from the true spirit andscope of the invention as defined by the appended claims.

1. A grating for as flooring in a clean room, the grate comprising abase plate having a plurality of holes therethrough that serve aschannels through which the air in the clean room is discharged, whereineach of the holes has a receiving portion open at one side of the baseplate and an exhausting portion open at the other side of the baseplate, the cross-sectional area of the receiving portion decreasing in adirection from said one side of the base plate toward the exhaustingportion, and the cross-sectional area of the exhausting portiondecreasing in a direction from said other side of the base plate towardthe receiving portion.
 2. The grate as set forth in claim 1, wherein thegrate has frusto-conical surfaces that define the receiving portion andthe exhausting portion, respectively, of each of the holes.
 3. The grateas set forth in claim 1, wherein the grate has curved surfaces thatdefine the receiving portion and the exhausting portion respectively, ofeach of the holes.
 4. The grate as set forth in claim 1, wherein each ofthe holes has a circular cross-sectional shape.
 5. The grate as setforth in claim 1, wherein each of the holes has an elongatecross-sectional shape so as to be in the form of a slot.
 6. The grate asset forth in claim 1, wherein each of the holes has a middle portionextending a finite distance between the receiving portion and theexhausting portion, the middle portion of the hole having a uniformcross section from the receiving portion to the exhausting portion. 7.The grate as set forth in claim 1, further comprising a tile ofpolyvinyl chloride attached to the top surface of the base plate.
 8. Thegrate as set forth in claim 1, wherein the total area of ends of theholes at said one side of the grate is about 18% of the total area ofsaid one side of the grate.
 9. The grate as set forth in claim 1,wherein the diameter of the widest portion of each of the holes is about10 mm, and the diameter of the narrowest portion of each of the holes isabout 8.5 mm.
 10. A clean room system comprising: a clean room having aceiling and a floor; at least one of a fan and a filter disposed in theceiling of the clean room; and grating disposed in the floor of theclean room, the grating defining a plurality of holes through which airinside the clean room is discharged through the floor of the clean room,the grating having one side exposed to the interior of the clean room,and another side facing away from the interior of the clean room, andthe cross-sectional area of each of the holes decreasing and thenincreasing in a direction from said one side of the grating to saidanother side of the grating.
 11. The clean room system as set forth inclaim 10, wherein each of the holes of the grating has a receivingportion open at said one side of the grating and an exhausting portionopen at the other side of the grating, the cross-sectional area of thereceiving portion decreasing in a direction from said one side of thegrating toward the exhausting portion, and the cross-sectional area ofthe exhausting portion decreasing in a direction from said another sideof the grating toward the receiving portion.
 12. The clean room systemas set forth in claim 11, wherein the grating has frusto-conicalsurfaces that define the receiving portion and the exhausting portion,respectively, of each of the holes.
 13. The clean room system as setforth in claim 11, wherein the grating has curved surfaces that definethe receiving portion and the exhausting portion respectively, of eachof the holes.
 14. The clean room system as set forth in claim 11,wherein each of the holes of the grating has a middle portion extendinga finite distance between the receiving portion and the exhaustingportion, the middle portion of the hole having a uniform cross sectionfrom the receiving portion to the exhausting portion.
 15. The clean roomsystem as set forth in claim 10, wherein each of the holes of thegrating has a circular cross-sectional shape.
 16. The clean room systemas set forth in claim 10, wherein each of the holes of the grating hasan elongate cross-sectional shape so as to be in the form of a slot. 17.The clean room system as set forth in claim 10, wherein the gratingcomprises a tile made of polyvinyl chloride at the top thereof.